As a green alternative for the traditional method of generating electrical energy, a photovoltaic cell module is employed to generate electricity by taking advantage of sunlight. The photovoltaic cell module is formed by assembling a variety of semiconductor component systems, and thus must be protected to alleviate the impact and damage from the environment such as moisture, oxygen, and ultraviolet. A typical structure of the photovoltaic cell module comprises a silicon wafer and protective layers laminated on both sides of the silicon wafer, wherein said protective layer may be a glass or a plastic film. Because of its excellent strength, weathering resistance, ultraviolet resistance and humidity insulation properties, back sheet formed by laminating a fluoropolymer film and polyester (PET) films plays an important role in the photovoltaic cell module. The traditional production of a back sheet involves adhering a pre-manufactured fluoropolymer film, especially a polyvinyl fluoride (PVF) film, to a polyester (PET) substrate, typically onto both sides of the PET film so as to form a sandwich-like structure. When a fluoropolymer film, e.g. a PVF film, is used as the back sheet for a photovoltaic cell module, its properties significantly improve the service life of the module, so that the service life of the module is ensured to be as long as 25 years.
However, it is difficult to obtain a sufficient adhesion between the pre-manufactured fluoropolymer film and the polymer substrate, such that a peel-off never occurs even after a few years of exposure to the outdoors. In the prior art, such as U.S. Pat. Nos. 3,133,854, 5,139,878 and 6,632,518, methods are described to obtain a durable back sheet having a laminated structure by pre-coating a ground layer or an adhesive layer on the substrate before adhering the fluoropolymer film. However, all of these methods need to provide at least one adhesive layer or ground layer prior to the actual laminating step, and then in the laminating step, the lamination is achieved by providing heat and pressure. Thus, the method comprising laminating a pre-manufactured fluoropolymer film involves quite a lot of steps and a relatively high cost. Meanwhile, the pre-manufactured fluoropolymer film must have a sufficient thickness to meet the requirements of its strength during the adhering and the post-processing process, which renders the actual thickness of the film thicker than that is necessary to provide the protection performance, resulting in waste of the expensive fluororesin film and increased cost of the product.